This application claims benefit of Japanese Patent Application No. 2000-304297 filed on Oct. 4, 2000, the contents of which are incorporated by the reference.
The present invention relates to packet switching and multicasting control systems used for the same and, more particularly, to multicasting control systems used in the case where multicast and unicast packets are switched together.
In a multicasting control system of this type, as shown in FIG. 7, a bit map table 35 stored with multicast output port data indicative of output ports which multicast packets are to be outputted from are stored, is accessed from a packet multiplexer 32.
Referring to FIG. 7, packets are sent out from input ports 301-0 to 301-n to input buffers 31-0 to 31-n. The input buffers 31-0 to 31-1 refers to multicast display bits and output port number bits stored in headers of the packets and tentatively accumulates them in their input buffers (not shown) for unicasting and those (not shown) for multicasting.
Subsequently, output requests are sent to output arbitrators (not shown) in the input buffers 31-0 to 31-n, and when the output arbitrators permit the output, the accumulated packets are sent to a packet multiplexer 32.
The packet multiplexer 32 multiplexes all the packets from the input buffers 31-0 to 31-n in predetermined fixed time slots, and then refers to the multicast display bits stored in the headers of the packets. When a multicast packet is identified, the bit map table 35 is retrieved on the basis of multicast packet connection number.
Multicast output port data obtained by the retrieval of the bit map table 35, are notified via a signal bus 303 to corresponding address filters 33-0 to 33-m, and the multicast packets are sent out to the time division basis multiplexed packet bus 302. When the inputted packets are unicast packets, the packet multiplexer 32 directly sends out the multiplexed packets to a time division basis multiplexed packet bus 302.
The packets sent out from the packet multiplexer 32 to the time division basis multiplexing path 302 are distributed to all the address filters 33-0 to 33-m. The address filters 33-0 to 33-m refer to the multicast display bits and output port number bits stored in the headers of the inputted packets.
When the inputted packets are unicast packets, the address filters 33-0 to 33-m take only packets, in each of which the output port number is identical with the own port address, and send the taken packets to output buffers 34-0 to 34-m.
When the inputted packets are multicast packets, the address filters 33-0 to 33-m each take only packets addressed to the pertinent output ports as detected from the multicast output port data received from the bit map table 35, and send out the taken packets to the output buffers 34-0 to 34-m.
The output buffers 34-0 to 34-m tentatively accumulate the received packets, and progressively send out these packets to output ports 305-0 to 305-m. When the number of the accumulated packets reach a threshold number, upon which a back pressure signal is to be sent out, the output buffers 34-0 to 34-m send out back pressure signals (i.e., congestion evasion signals) 304-0 to 304-m for evading the to the input buffers 31-0 to 31-n and stopping the sending of packets addressed to the output buffers 34-0 to 34-m.
In the above prior art multicast control system, when a back pressure signal is outputted from, for instance, the output buffer 34-0 in FIG. 7, it is sent to the corresponding one of the input buffers 31-0 to 31-n, which accumulates packets addressed to the output buffer 34-0, thus stopping the sending of packets addressed to the output ports 35-0.
Besides, since among the inputted multicast packets may be those addressed to the output buffer 34-0, the back pressure signal is also sent to the input buffers for multicasting in the input buffers 31-0 to 31-0, thus stopping the sending of the packets.
However, since the multicast packets may not be those addressed to the output buffer 34-0, it is possible to stop the sending of packets addressed to the output buffers, which have sent no back pressure signal.